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NORSOK Standard Z-008:2017
Language: English
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Risk based maintenance and consequence classification
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NORSOK Z-008:2017
This NORSOK standard is developed with broad petroleum industry participation by interested parties in the Norwegian petroleum industry and is owned by the Norwegian petroleum industry represented by the Norwegian Oil and Gas Association, The Federation of Norwegian Industries and The Norwegian Shipowners Association. Please note that whilst every effort has been made to ensure the accuracy of this NORSOK standard, neither the Norwegian Oil and Gas Association, The Federation of Norwegian Industries nor The Norwegian Shipowners Association, or any of their members will assume liability for any use thereof. Standards Norway is responsible for the administration and publication of this standard. Standards Norway P.O. Box 242 NO-1326 Lysaker NORWAY
Telephone: + 47 67 83 86 00 Email: [email protected] Website: www.standard.no/petroleum
Visiting address Mustads vei 1, NO-0283 Oslo Copyrights reserved
ICS: 913.18
Copyright protected document The material in this document is protected by copyright law. Without explicit authorization from Standard Online AS, reproduction is only allowed in so far as it is permitted by law or by agreement with a collecting society. Any publication in conflict with law or agreement, may result in liability to pay compensation and confiscation, and is punishable by fine or imprisonment. ii
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Contents Introduction....................................................................................................................................................................vi 1
Scope ....................................................................................................................................................................... 1
2
Normative references ....................................................................................................................................... 2
3
Terms, definitions and abbreviated terms ............................................................................................... 3
4
3.1
Terms and definitions......................................................................................................................................... 3
4.1
General ................................................................................................................................................................... 13
3.2
Methodology for risk based maintenance management ................................................................... 13 4.2
4.3
5 6 7
4.4
4.5
Risk decision criteria........................................................................................................................................ 14
Input to maintenance engineering ............................................................................................................. 15
Consequence classification .......................................................................................................................... 20 7.1
General ................................................................................................................................................................... 20
7.3
Consequence classification of main and sub function ........................................................................ 23
7.4
Principles and work flow ............................................................................................................................... 21
Documentation of consequence classification ...................................................................................... 24
Maintenance programme ............................................................................................................................. 25 8.2
8.2.1 8.2.2
General ................................................................................................................................................................... 25
Work flow for establishing preventive maintenance (PM) programme .................................... 25 Task selection...................................................................................................................................................... 25 Maintenance programme ............................................................................................................................... 26
8.3
Equipment characteristic unsafe failures................................................................................................ 26
8.5
Generic maintenance concept ...................................................................................................................... 27
8.4
Maintenance of technical barrier elements ............................................................................................ 27
8.5.1
General ................................................................................................................................................................... 27
8.6
Update maintenance programme /Continuous improvement ....................................................... 28
8.5.2
10
Static process equipment ............................................................................................................................... 14
Technical hierarchy ........................................................................................................................................ 20
8.1
9
Technical barrier elements ........................................................................................................................... 13
Maintenance management ........................................................................................................................... 16
7.2 8
Abbreviated terms ............................................................................................................................................ 12
8.6.1 8.7
Application of generic maintenance concepts (GMCs) ...................................................................... 28 Update maintenance programme ............................................................................................................... 29 Maintenance programme and handling of ageing ............................................................................... 30
Maintenance planning ................................................................................................................................... 31 9.1
9.2
Maintenance planning and scheduling ..................................................................................................... 31
Prioritising maintenance activities ............................................................................................................ 31
Reporting, analysis and improvements .................................................................................................. 33 10.1
General ................................................................................................................................................................... 33
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11
10.2
Reporting .............................................................................................................................................................. 33
10.4
Analysis and Improvement ........................................................................................................................... 34
10.3
Spare parts evaluation................................................................................................................................... 35 11.1
11.2
11.3
12
Key performance Indicators for maintenance management........................................................... 34
11.4
11.5
General ................................................................................................................................................................... 35
Work flow for evaluation of spare parts .................................................................................................. 35
Spare part categories ....................................................................................................................................... 36
Location and holding........................................................................................................................................ 36
Reorder level and order quantity ............................................................................................................... 37
Personnel and resources .............................................................................................................................. 37
Annex A (informative) Main function (MF) description and boundaries.............................................. 38 Annex B (informative) Simplifying consequence assessment of standard sub functions ............... 42 Annex C (informative) Risk assessment criteria ............................................................................................ 43 Annex D (informative) Practical examples ...................................................................................................... 47 Bibliography ................................................................................................................................................................. 56
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Foreword NORSOK Z-008:2017 was adopted as NORSOK Standard in December 2017. NORSOK Z-008:2017 supersedes NORSOK Z-008:2011.
NORSOK is an acronym for the competitive position of the Norwegian continental shelf and comprise petroleum industry standards in Norway. The collaboration initiative in 1993 between the authorities and the petroleum industry initiated the development of NORSOK standards. Reducing the project execution time and developing and operating cost for petroleum installations on the Norwegian shelf was the target.
The intention for the Petroleum industry is to develop and use standards providing good technical and cost effective solutions to ensure that the petroleum resources are exploited and managed in the best possible way by the industry and the authorities. The industry will actively contribute to the development and use of international standards in the global market. The NORSOK standards shall: • bridge the gap based on experiences from the Norwegian continental shelf where the international standards are unsatisfactorily; • replace oil company specifications where possible; • be available as references for the authorities’ regulations; • be cost effective; and • promote the Norwegian sector as an attractive area for investments and activities. Developing new NORSOK standards and regular maintenance of existing standards shall contribute to maintain the competitiveness both nationally and internationally for the Norwegian petroleum industry.
The NORSOK standards are developed by experts from the Norwegian petroleum industry and approved according to the consensus principles as laid down by the guidelines given in NORSOK A-001 N:2016 directive.
The NORSOK standards are owned by the Norwegian Oil and Gas Association, the Federation of Norwegian Industries and the Norwegian Shipowners' Association. They are managed and published by Standards Norway.
This NORSOK directive has been developed by Standards Norway in cooperation with the parties in the petroleum industry. All sections are normative. All Annexes are informative.
The following has been changed since last edition (revision 3, June 2011): • Changed scope to include all types of equipment in all types of installations • Updated references and terminology. ISO14224:2016 is used as the basis for maintenance terminology • Added section regarding input to consequence classification and maintenance engineering • Description of maintenance engineering of technical barrier elements • Better general description of work process for establish preventive maintenance programme • Review of standard to improve consistency of standard (shall, should and can) --`,,```,,,,````-`-`,,`,,`,`,,`---
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Introduction The purpose of this NORSOK standard is to provide requirements and guidelines for • establishment of technical hierarchy, • consequence classification of equipment, • how to use consequence classification in maintenance management, • maintenance management of technical barrier elements • how to use risk and reliability analysis to establish and update PM programmes, • how to aid decisions related to maintenance using the underlying risk analysis, • spare part evaluations.
This NORSOK standard is applicable for different purposes and phases such as: • design phase: establish initial maintenance programme as an input to manning requirements and system configuration. Selection of capital spare parts; • preparation for operation: development of initial maintenance programmes for implementation into maintenance management systems and selection of spare parts; • operational phase: updating and optimisation of existing maintenance programmes. Guidance for prioritising work orders. Lifetime extension. As a basis for preparation and optimisation of maintenance programmes for new and in service facilities all risk elements shall be taken into account, i.e. risks related to • personnel, • environment, • production loss, • direct and indirect cost including reputation.
This NORSOK standard is meant to define level of how this shall be done and deviations shall only provide better solutions with regards to maintenance management. This NORSOK standard should also be seen in conjunction with ISO 20815.
The standard describes the key work processes with explanation and requirements to each of them, and is organized in the following way:
Section 4: Methodology for risk based maintenance management
Section 5: Maintenance management
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Section 3: Terminology
vi
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Detailed methodology: Section 6: Technical hierarchy Section 7: Consequence classification Section 8: Maintenance programme Section 9: Maintenance planning Section 10: Reporting, analysis and improvements Section 11: Spare parts evaluation Section 12: Personnel and resources
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Annex A-D
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Risk based maintenance and consequence classification 1
Scope
The consequence classification and the maintenance task selection process can be applied to all types of items, and, in principle, all types of failure modes and failure mechanisms are covered by this NORSOK standard. However, for some types of items, other specific analysis should be performed to identify failure characteristics, failure frequencies and mitigating tasks. This include, among others, load bearing structures, static pressure equipment, risers and pipelines. This standard is developed with the oil and gas industry in mind, but the principles within can be applied to any industry, including manufacturing or processing plants, ships/maritime and energy plants/installations.
This NORSOK standard covers • definition of relevant nomenclature, • brief description of main work flow related to maintenance and which elements this typically involves, • definition of risk model and failure consequence classes, • guidelines for consequence classification, including − functional breakdown of plants and plant systems in MFs and sub functions, − identification of MF and sub function redundancy, − assessment of the consequences of loss of MFs and sub functions, − assignment of equipment to sub functions and associated consequence classes, • description of how to establish an initial maintenance programme, and how to update an existing programme, • description on how to use the classification in combination with probability for decision making related to prioritising work orders and handling spare parts.
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This NORSOK standard is applicable for preparation and optimisation of maintenance activities for all plant systems and items.
NORSOK Z-008:2017
2
Normative references
The following standards include provisions and guidelines which, through reference in this text, constitute provisions and guidelines of this NORSOK standard. Latest issue of the references shall be used unless otherwise agreed. For dated references, only the edition cited applies. Other recognized standards may be used provided it can be shown that they meet the requirements of the referenced standards. IEC 60300-3-11, IEC 60812, IEC 61508,
Dependability Management Part 3-11: Application guide – Reliability centred maintenance
Analysis techniques for system reliability - Procedure for failure mode and effects analysis (FMEA) Functional safety for electrical/electronic/programmable electronic safetyrelated systems
IEC 61511,
Functional Safety – Safety instrumented systems for the process industry sector
ISO 20815,
Petroleum, petrochemical and natural gas industries – Production assurance and reliability management
ISO 14224,
Petroleum, petrochemical and natural gas industries – Collection and exchange of reliability and maintenance data for equipment, Edition 3, Sept. 2016
NOG 070,
Guidelines for the Application of IEC 61508 and IEC 61511 in the petroleum activities on the continental shelf
ISO 17776,
ISO 13702,
NORSOK S-001,
NORSOK Z-013,
Petroleum and natural gas industries - Offshore production installations - Major accident hazard management during the design of new installations
Petroleum and natural gas industries – Control and mitigation of fires and explosions on offshore production installations – Requirements and guidelines
Technical safety Risk and emergency preparedness analysis
For informative references, see Bibliography.
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3 3.1
Terms, definitions and abbreviated terms Terms and definitions
For the purposes of this document, the following terms and definitions apply. 3.1.1 active repair time effective time to achieve repair of an item
Note 1 to entry: ISO 14224:2016 distinguishes between the terms mean active repair time (MART), mean time to repair (MTTR), mean time to restoration (MTTRes), and mean overall repairing time (MRT). See ISO 14224:2016 for further details. Note 2 to entry: The mean active repair time (MART) is defined as “expected active repair time” in ISO/TR 12489:2013, 3.1.34. See also ISO/TR 12489:2013, Figures 5 and 6.
3.1.2 availability ability to be in a state to perform as required
Note 1 to entry: See ISO 14224:2016, Annex C for a more detailed description and interpretation of availability. Note 2 to entry: Further terms are given in ISO/TR 12489:2013.
[SOURCE: ISO 14224:2016, 3.3]
3.1.3 barrier functional grouping of safeguards or controls selected to prevent a major accident or limit the consequences Note 1 to entry: Barriers can be subdivided into technical, operational and organisational barrier elements. Note 2 to entry: This document focuses on technical barrier elements.
[SOURCE: ISO 17776:2016, 3.1.1]
3.1.4 can expression in the content of a document conveying expected or conceivable material, physical or causal outcome. [SOURCE: NORSOK A-001:2016, A5]
3.1.5 condition-based maintenance preventive maintenance based on the assessment of physical condition
Note 1 to entry: The condition assessment can be by operator observation, conducted according to a schedule, or by condition monitoring of system parameters.
[SOURCE: ISO 14224:2016, 3.7] NORSOK © 2017
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[SOURCE: ISO 14224:2016, 3.2]
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3.1.6 condition monitoring obtaining information about physical state or operational parameters
Note 1 to entry: Condition monitoring is used to determine when preventive maintenance may be required.
Note 2 to entry: Condition monitoring may be conducted automatically during operation or at planned intervals.
[SOURCE: IEC 60050-192:2015, 192-06-28] 3.1.7 consequence outcome from an event
Note 1 to entry: There may be one or more consequences from an event. Consequences may range from positive to negative. However, consequences are always negative for safety aspects. Consequences may be expressed qualitatively or quantitatively. Note 2 to entry: Annex C.2 and ISO 14224:2016, Annex C.1.10 give examples of consequence classification.
Note 3 to entry: See also definition of Failure Impact in 3.1.17.
3.1.8 consequence classification qualitative analysis of events and failures and assignment of the consequences of these. Note 1 to entry: See definitions in 3.1.9, 3.1.10 and 3.1.11.
3.1.9 consequence HSE health, safety and/or environmental consequence of an event
3.1.10 consequence production effect with regard to production of a functional failure where effects of mitigation (e.g. spare parts, manning, tools) and compensation measures are not considered (= unmitigated consequence)
3.1.11 consequence other other consequences as a result of a functional failure other than HSE or production consequence Note 1 to entry: May also include monetary losses and loss of reputation.
3.1.12 corrective maintenance maintenance carried out after fault detection to affect restoration [SOURCE: ISO 14224:2016, 3.8]
3.1.13 critical failure failure of an equipment unit that causes an immediate cessation of the ability to perform a required function 4
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Note 1 to entry: See also ISO/TR 12489:2013, Figures 5 and 6, which illustrate terms used for quantifying corrective maintenance.
NORSOK Z-008:2017
Note 1 to entry: Includes failures requiring immediate action towards cessation of performing the function, even though actual operation can continue for a short period of time. A critical failure results in an unscheduled repair.
[SOURCE: ISO 14224:2016, 3.9]
3.1.14 degraded failure failure that does not cease the fundamental function(s), but compromises one or several functions
Note 1 to entry: The failure can be gradual, partial or both. The function can be compromised by any combination of reduced, increased or erratic outputs. An immediate repair can normally be delayed but, in time, such failures can develop into a critical failure if corrective actions are not taken.
[SOURCE: ISO 14224:2016, 3.11]
3.1.15 equipment class class of similar type of equipment units (e.g. all pumps)
Note 1 to entry: Annex A in ISO 14224:2016 gives equipment classes and also contains equipment-specific data for the equipment class.
[SOURCE: ISO 14224:2016, 3.18]
3.1.16 failure loss of ability to perform as required
Note 1 to entry: A failure of an item is an event that results in a fault of that item: see fault (3.1.17).
Note 2 to entry: A failure of an item is an event, as distinct from a fault of an item, which is a state [ISO/TR 12489:2013].
[SOURCE: ISO 14224:2016, 3.23]
3.1.17 failure cause set of circumstances that leads to failure
Note 1 to entry: A failure cause can originate during specification, design, manufacture, installation, operation for maintenance of an item.
Note 2 to entry: See also ISO 14224:2016, B.2.3 and Table B.3 which define failure causes for all equipment classes.
[SOURCE: ISO 14224:2016, 3.24]
3.1.18 failure frequency unconditional failure intensity; conditional probability per unit of time that the item fails between t and t + dt, provided that it was working at time 0 --`,,```,,,,````-`-`,,`,,`,`,,`---
Note 1 to entry: Another term used for failure frequency is “rate of occurrence”.
Note 2 to entry: See ISO 14224:2016, C.3 with respect to failure rate and failure frequency estimations.
Note 3 to entry: Note the difference between failure rate and failure frequency. Failure rate is defined in ISO 14224:2016, 3.32. NORSOK © 2017
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[SOURCE: ISO 14224:2016, 3.27]
3.1.19 failure impact effect of a failure on an equipment's function(s) or on the plant
Note 1 to entry: On the equipment level, failure impact can be classified in three classes (critical, degraded and incipient); see definitions of “critical failure”, “degraded failure” and “incipient failure” in ISO 14224:2016, 3.9, 3.11, and 3.40.
[SOURCE: ISO 14224:2016, 3.28] 3.1.20 failure mechanism process that leads to failure
Note 1 to entry: The process can be physical, chemical, logical, or a combination thereof.
Note 2 to entry: See also ISO 14224:2016, B.2.2 and Table B.2, which define failure causes for all equipment classes.
[SOURCE: ISO 14224:2016, 3.29] 3.1.21 failure mode manner in which failure occurs
Note 1 to entry: See also the tables in ISO 14224:2016, B.2.6 on the relevant failure modes which define failure modes to be used for each equipment class.
[SOURCE: ISO 14224:2016, 3.30]
3.1.22 failure rate conditional probability per unit of time that the item fails between t and t + dt, provided that it has been working over [0,t] Note 1 to entry: See also definition of failure rate in ISO/TR 12489:2013, 3.1.18.
Note 2 to entry: See ISO 14224:2016, C.3 with respect to failure rate and failure frequency estimations
Note 3 to entry: Note the difference between failure rate and failure frequency. Failure frequency is defined in ISO 14224:2016, 3.27.
3.1.23 fault inability to perform as required, due to an internal state
Note 1 to entry: A fault of an item results from a failure, either of the item itself, or from a deficiency in an earlier stage of the life cycle, such as specification, design, manufacture or maintenance. See also latent fault (ISO 14224:2016, 3.44).
Note 2 to entry: A fault is often a result of a failure of the item itself but the state can exist without a failure (see ISO 20815:2008, 3.1.14). Note 3 to entry: See also ISO/TR 12489:2013, 3.2.2. 6
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[SOURCE: ISO 14224:2016, 3.32]
NORSOK Z-008:2017
[SOURCE: ISO 14224:2016, 3.33]
3.1.24 generic maintenance concept GMC set of maintenance actions, strategies and maintenance details, which demonstrates a cost-efficient maintenance method for a defined generic group of equipment functioning under similar frame and operating conditions 3.1.25 hazard potential source of harm
Note 1 to entry: In the context of this NORSOK standard, the potential harm may relate to human injury, damage to the environment, damage to property, or a combination of these.
[SOURCE: ISO 17776:2016, 3.1.9]
3.1.26 hidden failure failure that is not immediately evident to operations and maintenance personnel
Note 1 to entry: Equipment failures that occurred at an earlier point of time, but were first observed at demand, fall into this category. Such failures are first revealed when the relevant functionality is tested (activated). Note 2 to entry: See definition with notes to entry in ISO/TR 12489:2013, 3.2.11. Note 3 to entry: See also latent fault (ISO 14224:2016; 3.44).
[SOURCE: ISO 14224:2016, 3.35]
3.1.27 incipient failure imperfection in the state or condition of an item so that a degraded or critical failure might (or might not) eventually be the expected result if corrective actions are not taken Note 1 to entry: The recording of incipient failure requires some criteria for when a fault of this nature requires registration as opposed to a state/condition where no corrective actions are required.
[SOURCE: ISO 14224:2016, 3.40]
3.1.28 inspection activity carried out periodically and used to assess the progress of damage in a component --`,,```,,,,````-`-`,,`,,`,`,,`---
Note 1 to entry: Inspection can be by means of technical instruments (e.g. NDT) or as visual examination.
Note 2 to entry: This document uses the common term “inspection” in the oil and gas industry, which relates inspection and inspection management to the activity of checking the conformity of the equipment by NDT instruments or visual examination at regular intervals.
[SOURCE: DNVGL-RP-G101:2010] 3.1.29 item subject being considered
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Note 1 to entry: The item can be an individual part, component, device, functional unit, equipment, subsystem, or system.
[SOURCE: ISO 14224:2016, 3.43]
3.1.30 main function MF principal tasks in a system being considered
Note 1 to entry: Annex A gives an overview of typical MFs for an oil and gas production plant.
3.1.31 maintainability ability to be retained in, or restored to a state to perform as required, under given conditions of use and maintenance Note 1 to entry: Given conditions would include aspects that affect maintainability, such as: location for maintenance, accessibility, maintenance procedures and maintenance resources. Note 2 to entry: See also ISO 14224:2016, Annex C for a more detailed definition and interpretation of maintainability.
[SOURCE: ISO 14224:2016, 3.47]
3.1.32 maintainable item item that constitutes a part, or an assembly of parts that is normally the lowest level in the equipment hierarchy during maintenance [SOURCE: ISO 14224:2016, 3.48]
3.1.33 maintenance combination of all technical and management actions intended to retain an item in, or restore it to, a state in which it can perform as required
Note 1 to entry: ISO 14224:2016, Figure 6 shows the main maintenance categories in more detail. ISO 14224:2016, Table B.5 presents the main types of maintenance activities commonly performed.
[SOURCE: ISO 14224:2016, 3.49] --`,,```,,,,````-`-`,,`,,`,`,,`---
3.1.34 maintenance effectiveness ratio between the maintenance actual result and performance target
Note 1 to entry: See examples of KPIs in Clause 10 and ISO 20815:2008, Annex E that can be used for measure of maintenance effectiveness.
3.1.35 maintenance management all activities of the management that determine the maintenance objectives, strategies, and the responsibilities and implement them by means such as maintenance planning, maintenance control and supervision, improvements of methods in the organisation including economical aspects [SOURCE: EN 13306:2010, 2.2] 8
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3.1.36 maintenance strategy management method used in order to achieve the maintenance objectives
[SOURCE: EN 13306:2010, 2.4] 3.1.37 may expression in the content of a document conveying consent or liberty (or opportunity) to do something
Note 1 to entry: Permissions are expressed using the verbal forms specified in ISO/IEC Directives Part 2 clause 7.4 Table 5.
[SOURCE: NORSOK A-001:2016, A.5]
3.1.38 modification combination of all technical and administrative actions intended to change an item
Note 1 to entry: Modification is not normally a part of maintenance, but is frequently performed by maintenance personnel.
Note 2 to entry: Care is needed to distinguish between maintenance due to failures and maintenance due to equipment modification.
3.1.39 performance standard PS measurable statement, expressed in qualitative or quantitative terms, of the performance required of a system, item of equipment, person or procedure, and that is relied upon as a basis for managing a hazard Note 1 to entry: Hardware performance standards address the functionality, reliability, survivability and interdependency of barriers under emergency conditions.
[SOURCE: ISO 17776:2016, 3.1.17]
3.1.40 predictive maintenance maintenance based on the prediction of the future condition of an item estimated or calculated from a defined set of historic data and known future operational parameters [SOURCE: ISO 14224:2016, 3.77]
3.1.41 preventive maintenance PM maintenance carried out to mitigate degradation and reduce the probability of failure
Note 1 to entry: Preventive maintenance contains condition-based maintenance and predetermined maintenance, see ISO 14224:2016, Figure 6.
[SOURCE: ISO 14224:2016, 3.78]
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[SOURCE: ISO 14224:2016, 3.67]
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3.1.42 production assurance activities implemented to achieve and maintain a performance that is at its optimum in terms of the overall economy and at the same time consistent with applicable framework conditions [SOURCE: ISO 20815:2008, 3.1.37]
3.1.43 redundancy existence of more than one means for performing a required function of an item
Note 1 to entry: See ISO 14224:2016, C.1.2 for further details, where passive (cold), active (hot) standby and mixed redundancy are described.
Note 2 to entry: Redundancy in IEC 61508:2010 is called “fault tolerance”.
[SOURCE: ISO 14224:2016, 3.80]
3.1.44 reliability ability of an item to perform a required function under given conditions for a given time interval [SOURCE: ISO 14224:2016, 3.81]
3.1.45 reliability centred maintenance RCM Systematic method for determining the respective maintenance actions and associated frequencies, based on the probability and consequence of failure [SOURCE: IEC 60050-192:2015, 192-06-08]
3.1.46 required function function or combination of functions of an item that is considered necessary to provide a given service [SOURCE: ISO 14224:2016, 3.1.83]
3.1.47 risk combination of the probability of an event and the consequence of the event
Note 1 to entry: See further important information regarding definition of risk in ISO 20815.
[SOURCE: ISO 20815:2008, 3.1.44]
3.1.48 risk based inspection RBI a decision making technique for inspection planning based on risk, compromising the probability of failure and the consequence of failure Note 1 to entry: These risks are managed primarily through equipment inspection.
[SOURCE: DNV-RP-G101:2010]
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3.1.49 safety system system which is used to implement one or more safety functions
Note 1 to entry: Safety function is in ISO/TR 12489:2013, 3.1.6 defined as “function which is intended to achieve or maintain a safe state, in respect of a specific hazardous event’. Note 2 to entry: Systems with safety functions are defined in ISO/TR 12489:2013, Annex A. These systems are also cross-related in ISO 14224:2016, Table A.3.
[SOURCE: ISO 14224:2016, 3.86]
3.1.50 shall expression in the content of a document conveying objectively verifiable criteria to be fulfilled and from which no deviation is permitted if compliance with the document is to be claimed Note 1 to entry: Requirements are expressed using the verbal forms specified in ISO/IEC Directives, Part 2 clause 7.2 Table 3.
[SOURCE: NORSOK A-001:2016, A.5]
3.1.51 should expression in the content of a document conveying a suggested possible choice or course of action deemed to be particularly suitable without necessarily mentioning or excluding others
Note 1 to entry: Recommendations are expressed using the verbal forms specified in ISO/IEC Directives, Part 2 clause 7.3 Table 4.
Note 2 to entry: In the negative form, a recommendation is the expression that a suggested possible choice or course of action is not preferred but it is not prohibited.
[SOURCE: NORSOK A-001:2016, A.5]
3.1.52 sub function grouping of items performing the same function within a main function
Note 1 to entry: See Annex B for a list of standardized sub functions.
3.1.53 tag/ tag number unique code that identifies the equipment function and its physical location [SOURCE: ISO 14224:2016, 3.91]
3.1.54 unsafe failure failure of a safety system which tends to impede a given safety action
Note 1 to entry: When dealing with safety instrumented systems, unsafe" is synonymous with "dangerous".
Note 2 to entry: An unsafe failure of an item is not necessarily a critical failure of the item. See further information in Clause 8.3.
[SOURCE: ISO/TR 12489:2013, 3.2.3] NORSOK © 2017
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3.2
Abbreviated terms
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API BOM CE CM CMMS EN FMECA GMC HSE IEC ISO KPI LCC LCP MF NDT NOG OEM OREDA® P&ID PM PS PSA PU QRA RBI RCM SIL
12
American Petroleum Institute bill of material Conformité Européenne corrective maintenance computerized maintenance management system European Standard failure mode, effect and criticality analysis generic maintenance concept health, safety and environment International Electrotechnical Commission International Organization for Standardization key performance indicator life cycle cost life cycle profit main function non destructive testing Norwegian Oil and Gas Association original equipment manufacturer offshore and onshore reliability data process and instrumentation diagram preventive maintenance performance standard Petroleum Safety Authority parallel unit quantitative risk analysis risk based inspection reliability centred maintenance safety integrity level
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4 4.1
Methodology for risk based maintenance management General
Risk assessment shall be used as the guiding principle for maintenance decisions. This document describes how to apply this in an efficient manner. The key elements of this methodology are as follows: a) consequence classification of functional failure; b) a risk based maintenance task selection process. Identification of relevant failure modes and estimation of failure probability should primarily be based on operational experience of the actual equipment. Alternatively generic failure data from similar operations may be used with sufficient reliability data qualification in accordance with ISO 20815, Annex E.2; c) use of Generic Maintenance Concepts (GMCs) in combination with classical RCM methods. The GMCs are developed by RCM analysis including plant experience. The GMCs will implicit express the probability of failure via the maintenance tasks and the maintenance interval assigned. It is recommended that the GMCs are adjusted to the local conditions via a cost-benefit assessment and including other local conditions; d) in case no GMCs are applicable or the purpose of the study requires more in-depth evaluations, an FMECA/RCM/RBI analysis shall be carried out; e) the application of the consequence classification and additional risk factors for decision making related to corrective maintenance and handling of spare parts. As important as the risk assessment, is having well defined work processes and company/management commitment. This document describes the main work flow and sets minimum requirements to each of the steps in this process. Further the process points out the importance of continuous improvement based on reporting and analysis of the plant condition.
Technical barrier elements
Safety and/or environmental barrier elements are defined as part of a major accident hazard management process, ref. ISO 17776 and NORSOK Z-013. The major accident scenarios are defined and barrier functions and barrier systems that prevents or mitigate the hazard are identified. Performance requirements are established as part of this analysis and the overall performance are documented in the form of Performance Standards (PS) or equivalent. The PS’ will set requirements with respect to availability, capacity and performance of barrier functions. Reference is made to NORSOK S-001, ISO 13702, IEC 61508, IEC 61511, NOG 070, ISO/TR12489 and ISO 20815. ISO 14224, F.4.2, lists the most common safety systems/components for an oil and gas installation with definition of critical/dangerous failure modes. Technical barrier elements are the physical items that realize one or several of the barrier functions.
One of the most important tasks for the maintenance organisation is to maintain this performance during the lifecycle of the plant. Availability requirements shall be used to determine the programme for PM activities and the required contingency plans in the event of failure. See Clause 7 for consequence classification of technical barrier elements. See Subclause 8.4 for maintenance of technical barrier elements.
The technical availability of the barrier functions shall be controlled and documented at all times. The development of failure frequency and system unavailability shall be used as the basis for changing of test intervals and other mitigating actions to ensure compliance with functional requirements. See Clause 10 for more information regarding reporting requirements. NORSOK © 2017
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4.2
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4.3
Static process equipment
Static process equipment has a dual function, i.e. a function related to storing or transporting gas or liquids, and a containment function related to preventing external leakage of gas and liquids. The functional requirement to the storing or transporting of gas and liquids are covered by document, see Clause 7.
In order to establish an inspection programme for the containment function of the equipment, it is necessary to perform detailed evaluations similar to a FMECA and RCM process, usually named RBI. The process requires knowledge of • failure mechanism which depends on material properties, internal fluid compositions and the external operational environment – determining the probability of failure, • consequence of leakage with respect to personnel, environment damages and financial losses.
The combination of the above represents the risk of failure which shall be mitigated.
The consequence classification methodology could be applied for screening of static mechanical equipment with the purpose of excluding non-critical equipment for further analysis and prioritise other equipment for in-depth risk evaluations as the basis for preparation of inspection programmes. The result of the RBI process is determination of • location and extent of inspections and condition monitoring, • inspection methods, • inspection intervals.
4.4
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There exist several standards for performing RBI analysis depending on type of object. Reference is made to DNVGL-RP-G101 for topside systems, DNVGL-RP-F206 for risers, DNVGL-RP-F116 for submarine pipeline systems and DNVGL-RP-0002 for subsea production systems. For refineries API RP 580 can be applied.
Risk decision criteria
Risk based decisions shall be done against defined criteria. The definition of the criteria should be done in accordance with overall company policy for HSE, production and cost. The criteria shall be properly defined and communicated to all personnel involved in risk decision, including operational personnel.
This document will not define any generic criteria, but describe an example of such criteria. See also NORSOK Z-013, ISO 17776 and ISO 14224. The level of detailing in any risk matrix used is company specific, and can typical vary from a course 3x3 matrix to a more detailed 5x10 matrix.
The following principles should apply: • the consequence- and risk matrices used for maintenance purposes should as far as possible be aligned with the overall company risk matrices but can be customized for maintenance purposes to aid proper planning and prioritizing of maintenance activities, and should be the same for all operations for a company in order to aid common companywide optimization and devote resources accordingly, as well as having a common terminology for communicating risk; • further, the same criteria should be used for all equipment and systems (also for equipment covered by other standards, such as load bearing structures, risers and pipelines). This is particularly important for topside maintenance and inspection planning which are handling basically the same hardware; • the consequence of loss of functionality (both loss of MF and sub functions) shall take into account the standby redundancy (see 3.1.43) and reduce the impact accordingly. Annex C gives example of criteria which can be used for classification, development of preventive work tasks and for prioritisation of work orders, as well as for optimisation of spare parts.
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4.5
Input to maintenance engineering
Maintenance engineering and the development of a maintenance programme should be considered as part of the design premises in an early stage of a projects phase, as decisions done in design will influence the level and type of maintenance necessary to perform when in operation. The designs effect on reliability, operation, maintainability and level of maintenance should be considered in all phases of design.
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Examples of relevant studies that can have input to the maintenance engineering include: • Barrier analyses (Performance Standards) (ref. NORSOK S-001 / ISO 13702); • Safety Integrity Level analyses (SIL) (ref. IEC 61508/61511, NOG 070); • Reliability analyses (ref. ISO 20815); • Risk Based Inspection analyses (RBI) (ref. DNVGL-RP-G101); • Life cycle cost/profit (LCC/LCP) (ref. ISO 15663); • Maintainability studies; • Working environment studies (ref. NORSOK S-002); • Material handling studies; • Manning studies; • HAZOP (ref. NORSOK Z-013).
See the individual sections for input and relevance of the various studies to maintenance engineering.
Before any detailed maintenance analysis is performed, proper design and operational documentation shall be in place.
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5
Maintenance management
The purpose of this clause is • to describe the key elements and expectations of the overall maintenance management work process, • to describe where consequence classification is applicable in the maintenance management work process, • highlight how risk management aspects are taken into account in the different steps in the process, • link the main steps to the rest of the document where risk assessment details are described. This description is not a comprehensive description of maintenance management in its wider sense. However, it gives a short description of what each step typically involves.
Maintenance management is illustrated as a work process where products are produced with low HSE risks and high production performance. The basic model proposed as industry best practice is shown in Figure 1 1.
On an overall level there are resources, management of work processes and results. Each of the elements in the management process may be detailed into a set of sub processes and products. In the following a brief description of the different elements in the maintenance management process is given. Those elements, where risk assessment, use of consequence classification and probability for failure assessment are important, are further described in this document and referenced below. Resources
Management of maintenance work process
Goal and requirements
Maintenance programme
Planning
Results
Maintenance execution
Organisation Risk level
Materials
Management and verification
Resource needs
Technical condition
Production assurance
Documentation and IT systems Improvements
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1
Analysis
Reporting
Figure 1 – Maintenance management process
The model is based on PSA “Basisstudie” from 1998
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Maintenance programme:
Goals should be established that commit the organisation to a realisable level of performance. The goals should focus on ambition level for • risk, production and cost, • regulatory requirements, • technical condition of the facility in particular the performance of safety systems and critical processes, • improvement of overall maintenance process. Maintenance strategies should be defined for the asset.
Failure modes, failure mechanisms and failure causes that can have a significant effect on safety and production shall be identified and the risk determined in order to establish a maintenance programme. The maintenance programme includes maintenance interval and written procedures for maintaining, testing, and preparing the various components within the plant as well as minimum qualification of personnel.
This activity will typically involve the following: • performing consequence classification for functions. The consequence class is inherited by the equipment relevant for the function; • for equipment representing high consequence in case of failure, the failure mode, failure cause and the connected maintenance programme shall be developed, documented and made traceable; • technical barrier elements shall be identified, reliability requirements defined for the functions, and a testing programme to maintain the functionality shall be developed; • criteria for when the maintenance programme are to be updated based on time, experienced failures or similar should be defined. In particular failures of safety critical systems shall be analysed and the programme updated on a regular basis. Planning:
See Clause 7 and Clause 8.
A maintenance plan is a structured set of tasks that include the activities, frequencies, procedures, resources and the time required to carry out maintenance. Planning consists of budgeting, long term planning, day to day planning and prioritising. This will typically involve the following: • have a defined method and criteria for planning and prioritising of both preventive and corrective work based on its impact on HSE and production; • group activities into efficient HSE and facility optimal groups/packages; • the plans are regularly monitored and reviewed to access achievement, backlog, and efficiency.
Maintenance execution:
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See Clause 9.
Execution includes preparations, work permits, carrying out work and reporting mandatory information on the work order. Maintenance and inspection work shall be executed in a safe and a cost-effective manner. System and equipment conditions shall be reported before/after repair for continuous improvement. Risk assessment shall be the basis for operational priorities. Licensee=/, User=, Not for Resale,
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Goals and requirements:
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This will typically involve the following: • work execution shall be performed by competent personnel according to plans, procedures and work descriptions relevant for the actual case; • the complexity of the work (both for individual jobs and for a set of jobs) should be taken into account; • a plan for verifying the quality of work executed should be in place; • the condition of the equipment should be reported after completion of work. For technical barrier elements with defined reliability targets, the failure data shall be reported to aid analysis and comparison vs. PSs. Reporting:
See Clause 10.
Reporting involves collection and quality assurance of maintenance data, and presenting these to maintenance departments and management in the form of defined indicators. In particular technical integrity data for barrier functions shall be known and reported at appropriate levels to aid decision making.
This will typically involve the following: • a set of KPIs shall be defined for monitoring and follow up of performance; • key performance indicator performance outside set goals should be reported and acted upon; • reports of safety performance, production and cost versus goals/budget should be available and communicated in the organization; • a set of performance data shall be reported and compared to established PSs. Analysis and Improvements:
See Clause 10.
This activity involves carry out analysis of historical maintenance data, and unwanted incidents related to maintenance, e.g. trend analysis, root cause failure analysis. Further the information should be evaluated and implement actions suggested based on the conducted analysis.
This will typically involve the following: • a defined analysis process shall be in place addressing trigger values, analysis technique and responsibilities. The work should be documented and monitored; • the analysis process shall include evaluation of maintenance effectiveness, i.e. to what extend the maintenance programme are handling the risks and performance requirements for individual systems or key components; • the identified improvements, actions should be implemented and the effect should be monitored. Organisation (Resources):
Materials (Resources):
See Clause 10.
The organisation consists of the people, their training, competence, job descriptions and work processes.
This will typically involve requirements to organisation, competence and roles/responsibilities.
Material resources include consumables, spare parts and tools required to carry out maintenance. --`,,```,,,,````-`-`,,`,,`,`,,`---
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This will typically involve that the spare part availability shall be optimized based on demand, consequence of failure, repair time and cost, and linked to the maintenance planning activity. Documentation (Resources):
See Clause 11.
Documentation in this context includes all documentation required to carry out and manage maintenance in an effective manner. This includes, but are not limited to, equipment/tag register, drawings and design details, historical maintenance data, maintenance task descriptions, spare part lists. This will typically involve the following: • maintenance data are organized into a database where technical information, plans and historic performance are readily available for users and decision makers; • this documentation needs to be controlled, updated and made available to the relevant user.
Management and verification:
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Risk level (Technical condition): Production assurance (Technical condition): Cost (Technical condition):
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A key to good maintenance is a well organized management team taking responsibilities in implementing the principles herein and verifying the results. The management team shall ensure that the maintenance work processes are followed.
This will typically involve the following: • the leaders shall define roles and responsibilities and qualification requirements within the area of maintenance; • the leaders shall possess knowledge related to risk based maintenance management and make sure that the main work flow is followed; • the leaders shall monitor defined indicators (KPIs) and act upon deviations from set goals; • in addition, the leaders should plan and institute audits of the organisation, suppliers and contractors. The risk level is a result of the operation and maintenance work done to the asset. Risk can be measured as HSE performance, technical barrier element reliability status or related indicators.
The plant’s production assurance is a result of the activities implemented to achieve and maintain a performance that is at its optimum in terms of the overall economy and at the same time consistent with applicable framework conditions. An indicator of this would be the achieved production availability. Cost is here related to man cost for preventive and corrective work, spare parts and consumables, lost/deferred production that is under the control of the maintenance function.
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6
Technical hierarchy
The technical hierarchy is a corner stone in maintenance management. It describes the technical structure of the installation by giving physical items unique identifiers. The technical hierarchy provides an overview of equipment units that belong together technically, and shows the physical relationship between main equipment, instruments, valves, etc. The technical hierarchy should be established at an early phase to give an overview of all the tags/equipment and how they are related. The purpose of the technical hierarchy is as follows: • show technical interdependencies of the installation; • retrieval of tags, equipment and spare parts; • retrieval of documents and drawings; • retrieval of historical maintenance data from CMMS; • planning of operations (e.g. relationships due to shutdown etc.); • cost allocation and retrieval; • planning and organization of the maintenance programme; • planning of corrective work.
The level on which the maintenance objects are established is governed by practical execution and the individual need to monitor and control the different maintenance programmes. The technical breakdown of an installation shall as a minimum be broken down to a level were requirements and history can be linked to the individual technical barrier elements, and that the performance of the technical barrier elements can be reported and verified.
See Annex D for detailed information and practical examples of the work process for establishing a technical hierarchy. Reference is made to public coding standards: • NORSOK Z-DP-002 • ISO 14224
7
7.1
Consequence classification General
This clause describes how consequence classification shall be done, its workflow and relation to maintenance programmes. Consequence classification expresses what effect loss of function can have on HSE, production and cost/other. The classification is done according to a consequence scale which is a part of the risk model, see Clause 7 and Annex C.
The consequence classification together with other key information and parameters gives input to the following activities and processes: • selection of equipment where detailed FMECA/RCM/RBI analysis is recommended (screening process); • establish PM programme; • preparation and optimisation of GMCs; • design evaluations; • prioritisation of work orders; • spare part evaluations. 20
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For corrective maintenance, where the work orders can be assigned to any tagged equipment, the cost will be traceable to a lower level, but even this costing should be possible to summarise to the same level as for the maintenance objects used for the PM programmes.
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7.2
Principles and work flow
Figure 2 shows an overall workflow related to classification.
The following principles apply: • The consequence classification is done to identify critical equipment for HSE, production and cost; • All physical tags/items shall be assigned a function and have a consequence classification, and no items or systems should be screened out based on an “assumed” low consequence. Administrative tag/items (e.g. systems, areas, equipment classes) used for establishing a technical hierarchy do not have to be classified. However, if they have preventive or corrective work orders assigned to them they should be classified to get proper prioritization in the maintenance management system; • All systems and/or tags related to an installation shall be classified using the same classification scale – regardless which method and standard is used for the classification; • The classification feeds in to a common risk model used for operational decision making thus they need to be comparable; • A functional hierarchy is established (MFs and sub functions). This is normally not stored in the CMMS but used during the classification process. See Annex D.2 for an example of a functional breakdown of a system. Equipment/maintenance objects are assigned to the relevant sub function; • The consequence of loss of containment is assessed as a separate failure mode from the loss of function; • Barriers are defined via safety analysis (e.g. quantitative risk analysis) in the design or modification process. As such these systems and equipment are already identified and its safety function defined, normally with high consequence for HSE; •
•
•
Note to entry: Barrier functions identified as part of a major accident hazard management process can be different from main- and sub functions in the consequence classification process described in this document.
Technical barrier elements shall be marked in the maintenance management system, and if not done as part of the barrier analysis, can be done as part of the consequence classification analysis based on the barrier analysis. This will typically be which performance standard(s) the item is part of; The consequence classification only assesses the primary function of an item (i.e. pumping, storing) and not classification of failure characteristics of a function or item, like explosion proofing, overheating, short circuiting, which are considered as failure modes- or mechanisms of the item/function. See Subclause 8.3 for more information; The outcome of the classification will be a set of attributes assigned to each tag. The set of parameters shall be aligned to the decision model. Examples of information to be assigned to each tag are − functional failure/loss of function – HSE consequence, − functional failure/loss of function – production consequence, − functional failure/loss of function – cost/other consequence, − consequence of loss of containment, − barrier function identifier, − redundancy.
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Consequence classification process Design documentation
Documentation: Tag information Technical hierarchy (Clause 7) • Operational data
Identify Main- and Sub Functions
Consequence classification
Assigning item/tags to functions
Documentation and output
• •
Identify main Functions
• •
Identify Sub Functions Relevant analysis: • Barrier analysis • RBI • Reliability studies Others, ref. Clause 4.5
• • • Assign consequences and redundancy level to main- and sub functions
•
Assign item/tag to sub functions
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Input to: Spare part analysis (Clause 11) Prioritizing of CM (Clause 9.2) RBI Reliability analysis Risk Mgt. system KPIs (Clause 10)
Outcome per tag: HSE conseq. Prod. conseq. Other conseq. Redundancy Containment conseq. • Barrier function id • • • • •
Establish preventive maintenance program (Clause 8)
Figure 2 – Consequence classification process
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7.3
Consequence classification of main and sub function
The functional classification work process is described stepwise below, and illustrated in Figure 2. No
Step
Activity
1
Technical information
•
2
Input from other analyses
• •
• • 3
Identify MFs
• •
•
4
Identify sub functions
• •
5
6
Assign MF redundancy
• •
Assign MF • consequences • •
Technical information and documentation regarding systems and items is used to identify systems and equipment which is subject to consequence classification. The Technical Hierarchy is beneficial for establishing an overview of the technical relationship between the items. See Clause 6 regarding technical hierarchy.
See Subclause 4.5 for information regarding documentation and relevant studies. Barriers are identified via a risk assessment where performance requirements are defined such as reliability and survivability. In the classification process these systems are mapped to the relevant items for readily identification in the CMMS system. The functional requirements are carried forward to the maintenance programme to maintain these functions. Containment: For the tags/systems that are containment related, results from a RBI analysis can be used as a guide to the consequence of loss of containment. Availability: Production assurance studies (e.g. RAM) can give input to functions critical to the operation of the installation. Each plant system is divided into a number of MFs covering the entire system. The MFs are characterised by being the principal tasks in the process such as heat exchanging, pumping, separation, power generation, compressing, distributing, storing, etc. Annex A gives an overview of typical MFs for an oil and gas production plant. Each MF is given a unique designation consisting of a number (if appropriate a tag number) and a name that describes the task and the process.
MFs are split into sub functions. In order to simplify the consequence assessment, the sub function level can be standardised for typical process equipment with pre-defined terms. See Annex B. The standard list of sub functions has to be supplemented with other sub functions relevant for the system configuration. MF redundancy shall be specified, see Table C.2 for example of redundancy definitions. In case of safety systems or protective functions with redundancy due to functional reliability or regulatory requirements, the redundancy effect should not be counted for.
The entire MF failure consequence is assessed in terms of the state where the MF no longer is able to perform its required functions. Assuming that other adjacent functions and equipment are operating normally. In this assessment any redundancy within the function is disregarded, as the redundancy will be treated separately. --`,,```,,,,````-`-`,,`,,`,`,,`---
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No
Step
Activity • •
7
Assign sub function redundancy
8
Assign sub • function consequences
9
Equipment mapping to function
•
• • •
10
7.4
Result per equipment
•
Other mitigating actions are not considered at this stage, i.e. like spare parts, manning, and tools. The most serious, but nevertheless realistic effects of a function fault shall be identified according to set risk criteria. See Subclause 4.4.
If there is redundancy within a sub function, the number of parallel units and capacity per unit shall be stipulated, see Table C.2 for example of redundancy definitions. The consequence on system/plant of a fault in a sub function is assessed with respect to HSE, production and cost according to the same principles as outlined for MF.
The equipment (identified by its tag numbers, see Clause 6) carrying out the sub functions are assigned to the respective sub functions. If equipment performs more than one sub function (e.g. some instrument loops), it is assigned to the most critical sub function. All equipment (identified by its tag number) will inherit the same description, consequence classification and redundancy as the sub function of which they are a part. See Annex C for an example. Consequence analysis shall be documented according to Subclause 7.4 and the key data be available in the CMMS.
Documentation of consequence classification
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A sound principle is to make the assessment available and traceable for updates and improvements of the results, as more information and feedback from the operation become available. As a minimum, the following shall be documented: • decision criteria; • definition of consequence classes; • MF description; • sub function description; • assignment of equipment (tags) to sub function; • assessment of the consequences of loss of MFs and sub functions for all consequence categories, including necessary arguments for assignment of consequence classes; • assessment of MF and sub function redundancy; • any deviations shall be documented and explained.
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8
Maintenance programme
8.1
General
This clause describes how the consequence classification shall be used to establish a risk based preventive maintenance programme. The purpose of a maintenance programme is to control or mitigate risks associated with degradation of a function. Maintenance activities includes predetermined- and condition based activities. The programme shall include activities and maintenance intervals per item. The consequence classification, as described in Clause 7, shall be used as a basis for the selection of the maintenance activities and –intervals.
The maintenance programme shall be risk based and critical failure modes shall be managed at all times and mitigated when necessary. Using Generic Maintenance Concepts (GMC) is an efficient and cost effective way of developing a risk based maintenance programme, see Subclause 8.5.
8.2
8.2.1
Work flow for establishing preventive maintenance (PM) programme Task selection
The results from the Consequence Classification as described in Clause 7 shall be used as an input to the preventive maintenance programme task selection process. This analysis can typically be a screening for which items to analyse further in more detail. The task selection process is shown in Figure 3 and described below. Consequence classification
Failure mode analysis
High
Risk analysis
High
Task selection
Medium/ Low
Medium/Low
Preventive maintenance
Cost/benefit analysis
Planned corrective maintenance
Risk Based Inspection analysis
Containment
Figure 3 – Establishing maintenance programme for new plants For items classified with high consequence of failure on HSE the items’ failure modes shall be identified and analysed with respect to the effect on the item functionality. This should also be done for items classified with high consequence of failure on operation or cost, in order to maintain operational regularity and reduce cost. --`,,```,,,,````-`-`,,`,,`,`,,`---
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The recommended approach is to perform a Failure Mode Effect and Criticality Analysis (FMECA) to identify critical failure modes and the contributing failure mechanisms that needs to be controlled or mitigated. See IEC 60812 (or similar standards) for more information on how to perform a FMECA analysis.
Failure modes identified in the failure mode analysis that are critical to the function of the item shall be controlled or mitigated. This should be done using a Reliability Centred Maintenance (RCM) approach, where the failure characteristics are analysed to identify the optimal method to control or mitigate the failure mode under development. This can include hidden failures, the possibility to detect failure, failure patterns, the availability of condition monitoring, etc. See IEC 60300-3-11 (or similar standards) for more information on how to perform a RCM analysis.
Failure modes that are not critical to the function of an item, as well as items performing functions that do not have significant effect on safety, external environment, working environment, operation or cost can be assigned minimum maintenance requirements to prolong the lifetime of the item based on a cost-benefit analysis. This can include operational procedures, cleaning, lubrication, simple verification tests, etc.
Items with medium or low consequence of functional failure may still have failure modes that render them unsafe in operation and which needs to be controlled or mitigated. See Subclause 8.3 for more information.
The maintenance task intervals should be based on knowledge and experience from similar items operating under similar conditions, and then be adjusted when experience is gained for the specific installation/items.
For items with similar failure modes and -mechanisms, and operating under similar conditions, Generic Maintenance Concepts (GMC) can be developed in order to perform the task selection process more efficiently. See Subclause 8.5 for more information. 8.2.2
Maintenance programme
The identified preventive maintenance tasks shall be scheduled in a maintenance management system.
In establishing the preventive maintenance programme the impact on operation should be minimized. E.g. possibilities for condition monitoring, establishing efficient work packages, group similar maintenance task into maintenance campaigns and planning of intrusive maintenance to planned shutdowns/turnarounds.
In developing the maintenance programme local knowledge and experience shall be utilized. This could include working environment, work load, maintainability, etc. The created work orders shall as a minimum contain information about priority, start-/end date, overdue date, required spare parts and resources, personnel, task duration, shutdown requirements, etc. for proper planning and follow up of maintenance. See Clause 10.2 for more information.
8.3
Equipment characteristic unsafe failures
Some items may suffer failure modes that render them unsafe in operation but which do not harm the functionality of the item. Example is damage to electrical insulation causing short circuit dangerous for personnel touching the item. The electrical failure is usually not considered a functional failure but represents a dangerous situation. These failure modes or failure mechanisms related to the 26
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If no preventive maintenance or assurance activities are identified to be required or cost effective, the item or failure mode may be assigned a planned corrective maintenance strategy.
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characteristics of an item shall be identified and be assigned probability and consequence, as well as preventive maintenance tasks to control the risk.
This is best identified in a task selection process as described in Subclause 8.2.1 and can be documented as part of a Generic Maintenance Concept (see Subclause 8.5).
The CE (Conformité Européenne) marking of equipment shall include an assessment of personnel risk as part of the information for use. Relevant standard is ISO 12100.
8.4
Maintenance of technical barrier elements
Safety- and environmental barriers are usually defined in barrier analysis based on ISO 13702 and NORSOK S-001. The items performing a barrier function needs to be identified and the selection of maintenance task for items with a barrier function (safety and/or environment) are based on the same work process as other items, as described in Subclause 8.2 (i.e. identification of failure modes and activities to control or mitigate these failure modes).
The performance of the technical barrier element shall be described so a maintenance operator can test, verify and report the condition of the item performing the barrier function. This especially applies to technical barrier elements with hidden failures (dangerous undetected failures) which are not normally evident to operation- and maintenance personnel. For items with function tests to detect dangerous undetected failures, the maintenance work order in the maintenance management system shall as a minimum then contain: • description and requirements of test (e.g. no maintenance before function test); • failure characteristics (e.g. valve do not close within specified time); • acceptance criteria (e.g. closing time 12 seconds); • how the result of a failure shall be reported (e.g. “create notification in CMMS with failure mode Fail To Close”). A system shall be in place to analyse test results and verify that the availability of the barriers are in accordance with design and operational requirements, typical SIL requirements and Performance Standards.
8.5
Generic maintenance concept
Performing FMECA- and RCM analysis on all items with high consequence individually on an installation can be costly and time consuming. Using Generic Maintenance Concepts (GMC) is an efficient and cost effective way of developing a risk based maintenance programme, standardizing maintenance activities and capturing and sharing company experience and knowledge. 8.5.1
General
A GMC is a set of maintenance actions, strategies and maintenance details, which demonstrates a costefficient maintenance method for a defined generic group of items functioning under similar frame and operating conditions. The use of the GMC shall ensure that all defined HSE, production, cost and other operating requirements are met. The concept should include relevant design and operating conditions and should be documented by a FMECA/RCM analysis. A generic concept can be seen as a collection of best practices for a company, and as such should be maintained and updated via a controlled process as new experience and technology becomes available, see Annex D.
For barrier functions: the performance requirements, the corresponding acceptance criteria and critical failure modes shall be defined on the concepts. The GMC shall be established based on the same task selection work process as described in Subclause 8.2 for individual items, but performed on a generic group of items and include recommended --`,,```,,,,````-`-`,,`,,`,`,,`---
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maintenance interval and maximum allowed interval. See Annex D for an example of how to document GMCs. The extent of documentation will differ depending on the complexity of the equipment and the risk attached. 8.5.2
Application of generic maintenance concepts (GMCs)
Generic maintenance concepts may be developed in order to • establish a company’s minimum requirements to maintenance, • reduce the effort in establishing the maintenance programme as similar items/technologies are preanalysed, • ensure uniform and consistent maintenance activities, • facilitate analysis of group of items, • provide proper documentation of selected maintenance strategies, • ensure experience transfer between plants with similar technology and operation. Generic maintenance concepts are applicable for all types of items covered by this document.
A GMC can be utilized when • the group of equipment has similar design, • the equipment has similar failure modes, failure frequencies and operating conditions, • the amount of similar equipment justifies the development of a generic concept.
In case of significant differences between the actual equipment and the equipment which has been the basis for the GMCs, the equipment in question has to be treated individually as a separate generic class of equipment. Basically, equipment failure modes are independent of equipment functionality, i.e. which functions the equipment supports. However, operational conditions, location and external environmental impact may influence the probability of failure and should be assessed prior to use of GMCs.
For complex equipment packages with a high consequence in case of failure, like gas turbines, top drives and offshore cranes, a complete FMECA/RCM should be performed for each individual equipment package in order to capture the complexity of these kind of items. However, for individual items that are part of the complex item, like valves, transmitters, etc. the general maintenance concepts can be used as input to the analysis of the complex item.
8.6
Update maintenance programme /Continuous improvement
A continuous improvement process shall be in place in order to enhance safety levels and at the same time reduce down time and cost. Reference is made to the Clause 5 and Figure 1 – Maintenance management process.
A set of objectives or requirements for the maintenance performance shall be established in order to measure maintenance performance. This shall include acceptance criteria for safety, availability and cost. From a plant wide perspective it shall be possible to break these acceptance criteria down to system and item/equipment class levels (co-related targets) and were the performance of the individual technical barrier elements can be verified.
It should be possible to extract the necessary technical information from the maintenance management system in order to analyse the effectiveness of the maintenance. This can further be supplemented by input from maintenance and operational personnel. Reference is made to Clause 10 for reporting, KPIs and analysis. 28
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Expected corrective maintenance, required resources and spare parts can also be added to the GMC and thus make the GMC a tool for benchmarking and input to design and operational and maintainability studies.
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8.6.1
Update maintenance programme
A maintenance programme shall be reviewed and updated at regular intervals. The triggers for such updating can be one or more of the following: • the observed failure frequency is significantly different from what was expected, i.e.: − higher failure frequency is observed requiring a change in maintenance strategy or maintenance frequency – or replacement of the unit; − lower failure frequency, or no observed damage at PM may point towards extension of intervals or omitting certain tasks. • the operational environment has changed causing different consequence and probability: − less or more production; − change in product composition. • cost of maintenance different from expected: − new technology that could make the maintenance more efficient (like new methods for condition monitoring) is available; − updated regulations; − information from vendor; − modifications or replacement with new equipment.
The evaluation shall be based on historical data and experience. A process diagram to update a maintenance programme is shown in Figure 4. If it is a safety system, an evaluation of number of failures per tests versus PS requirements shall be performed. If there is a significant change in the safety system performance stated in the PS, this information shall be fed back to the overall risk assessment for the plant. For non-safety systems a cost-benefit analysis based on experience should be performed. Based on this evaluation maintenance programme and GMC (if relevant) should be updated, and implemented in the maintenance plan.
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Data/ experience from operation and maintenance
Update safety analysis as necessary (QRA, SIL, PS, etc.)
Update production assurance analysis as necessary
Barrier safety function
Analyse historical failure data vs. Performance Requirements
Update maintenance activities: frequency, man-hrs, work description, etc.
Analyse historical failure data. Cost-benefit of PM vs. Risk
New/update generic maintenance concept (if relevant)
Yes
No
Update maintenance program as necessary
Figure 4 – Process for updating maintenance programme
8.7
Maintenance programme and handling of ageing
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Most maintenance programmes are based on a relatively constant failure frequency and not considering the ageing development that systems can suffer. However, the maintenance function shall at any time have an overview of the ageing development for its components, and do maintenance and upgrading to ensure safe and reliable operation. The same principles for continuous improvement, as described in Subclause 8.6, can be used. However the continuous improvement process might not have the same long term view and take into account simultaneous failures that come into effect when the installation is reaching its intended lifetime.
The cost regarding aging and displacement or restoration of an item should be taken into consideration in the Life Cycle Cost (LCC) analysis (ref. ISO 15663), preferably in the design phase. In the operation phase a register of risk ranked vulnerabilities can be made with expected future operating cost and modification/capital cost requirements. A more dedicated effort may be required when approaching the intended lifetime for the plant. Such an effort involves the following: a) evaluate operational and degradation history. Any incidents with large degradation, abnormal operation, etc. should be identified as well as any detrimental effect of modifications done to the unit. Collection and verification of system documentation and “as-build” documentation; b) assessment of current condition/”as-is” condition; c) evaluate the future ageing in view of the planned future operation and load planned for the asset: 1) are there any ageing phenomena that have not been seen so far but are under development? 2) are the barrier function status and development according to requirements? 3) will any items/system become obsolete so that spare parts no longer can be purchased? d) based on c) decisions need to be made regarding: 30
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1) any updates to the maintenance programme (and GMC as necessary) or changes in the spare part holding strategy, 2) replacement or modifications of single components or larger units, 3) any operational constrains for the unit in view of ageing, 4) dedicated analysis for e.g. structure.
See NOG 122 for required documentation of maintenance and inspection in connection with formal application for consent of extended lifetime.
9
9.1
Maintenance planning
Maintenance planning and scheduling
There shall exist a maintenance plan covering both preventive and corrective maintenance. Safety critical and/or operation critical maintenance activities shall be included in the installation total activities plan.
The PM programme is established as described in Clause 8. This programme consists of a list of preventive maintenance activities and intervals for a plant. In order to facilitate proper planning the preventive maintenance work orders should be generated in the CMMS in due time. Planning of preventive and corrective work orders shall include the necessary preparation for the activity, such as materials, personnel, tools, access, impact on operations, etc.
9.2
Prioritising maintenance activities
Criteria for setting the priorities and deadlines for maintenance activities shall be established. This shall be based on the consequence classification, failure impact, failure development time and mitigating measures. Prioritizing of planned and corrective maintenance activities should be aligned.
Preventive maintenance work orders are based on risk and failure frequencies for the failure mode and should in principle be executed according to the given maintenance plan. Backlog related to the plan shall be prioritised based on risk, i.e. probability and consequence of failure.
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Prioritization of corrective maintenance shall be done based on the risk the failure represents, described as consequence and failure impact/probability of failure. Some companies call this process “Risk Based Work Selection”, and have implemented it in their maintenance management system. Figure 5 shows an example of such a work flow, i.e. a selection of which corrective work orders to prioritize.
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Failure impact for the give case Create failure report for equipment with description of failure
Risk model with criteria for action
Priority of work orders
Consequence of failure for the given case
Consequence classification of equipment
Figure 5 – Priority of corrective work orders
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The process involves the following: • assigning the consequence of failure to the case. It can be assigned via the consequence classification of equipment on overall functional level. This consequence shall always be supplied by information regarding the actual failure mode, the operational state of the plant, possibilities for rerouting the process, etc. As such the process cannot be automatic, but requires involvement from personnel knowing the plant and the actual case. E.g. unsafe failure modes (see Subclause 8.3) for low consequence equipment; • assigning the failure impact, see Table 1 and Subclause 3.1 Terms and definitions. A time to failure scale may also be used, see Table C.3; • for failure impact “degraded or incipient failure”, a time to failure shall be assigned and used in the setting of priority (time) for the repair work; • the risk associated with the consequence and probabilities as well as actions from this risk (priorities) shall be defined in given criteria e.g. via a risk matrix. Table C.3 shows an example of a risk model described as a risk matrix used to determine the priority; • priority. Compensating operational actions used to temporarily maintain the function can be described as redundancy; • compensating measures shall be in place when failure on the safety critical functions.
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Table 1 – Failure impact scale Failure impact
Definition
Critical failure
Degraded failure
Incipient failure
Failure of an equipment unit that causes an immediate cessation of the ability to perform a required function.
Failure that does not cease the fundamental function(s), but compromises one or several functions. Imperfection in the state or condition of an item so that a degraded or critical failure may (or may not) eventually be the expected result if corrective actions are not taken.
Note Includes failures requiring immediate action towards cessation of performing the function even though actual operation may continue for a short period of time. A critical failure result in an unscheduled repair.
The failure can be gradual, partial or both. The function can be compromised by any combination of reduced, increased or erratic outputs. An immediate repair can normally be delayed, but in time such failures may develop into a critical failure if corrective actions are not taken.
10 Reporting, analysis and improvements 10.1 General Reporting and analysis of maintenance performance is required in order to ensure continuous improvement. Below is described how this should be done.
10.2 Reporting
Table 2 shows some relevant failure and maintenance data related to maintenance activities, that as a minimum should be recorded. The ISO 14224 standard gives requirements and recommendations for reporting of data related to maintenance, see ISO 14224 for a more complete overview and further details. The need for reporting will vary between systems and equipment, and need to take into account field personnel resource utilisation. Table 2 – Reporting of failure and maintenance data
Failure data
Maintenance data
Failure date
Maintenance category (PM, CM)
Failure mode
Condition of equipment before and after maintenance
Failure cause
Spare parts used
Failure mechanism
Maintenance man-hours for activity
Failure impact
Start and finish time of activity
Detection method
Equipment down time
Operating condition at failure
Active maintenance time
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10.3 Key performance Indicators for maintenance management KPIs shall be defined to support the overall goal and strategy for the operational phase. This will indicate the current status of the maintenance being performed and the effectiveness of the maintenance organisation, and support continuous improvement.
Setting up the right set of KPIs facilitates people to focus and prioritise in the same direction. A combination of reactive (lagging, backward-looking) KPIs and proactive (leading, forward-looking) KPIs should be selected. Examples of some relevant KPIs are shown below:
Table 3 – Examples KPIs
KPI
Purpose
Preventive maintenance workload
Indication of amount of preventive maintenance work
PMs overdue
Indication of outstanding PM backlog
Both number of work orders and man-hours should be recorded
Indication of outstanding CM backlog
Both number of work orders and man-hours should be recorded
HSE critical PMs overdue CMs overdue
HSE critical CMs overdue Failure fraction
Indication of amount of corrective maintenance work Indication of outstanding HSE critical PM backlog Indication of outstanding HSE critical CM backlog
Average unavailability (PFDavg) due to dangerous undetected failures is established by using test reports
Both number of work orders and man-hours should be recorded Both number of work orders and man-hours should be recorded
Target failure fraction should be based on risk- and barrier analysis
See ISO 14224, Annex E, and EN 15341 for examples of relevant KPIs.
Key KPIs should be measured continuously where possible. Other KPIs that require more information gathering should be updated at set regular intervals. Targets for KPIs should be set within a timeframe that is achievable and where any corrective actions will have taken effect.
Targets for KPIs related to unavailability of safety critical equipment shall be based on relevant riskand barrier analysis.
10.4 Analysis and Improvement
Based on reported maintenance data the effectiveness of maintenance shall be evaluated systematically.
The organization shall have an established set of key performance indicators to evaluate against – KPIs reflecting the goals and requirements for the operation, see Clause 5. For practical reasons some trigger levels should be applied above which a more detailed investigation is done aiming at finding the rootcause for the failure. The triggers can be related to: • HSE related equipment failure; • unacceptable production losses; • cost of single failure events in terms of downtime, repair cost or spare cost; • number of repeated failures over a given time period for key components; 34
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Corrective maintenance workload
Comment
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• •
hidden failures (exceeding requirements) detected during test; technical condition assessments.
Based on the event(s) the root cause(s) should be identified and necessary actions taken to avoid reoccurrence. The problem at question can be either single discipline or multidiscipline. The team should be allocated to the actual case, and will typically consist of personnel operating the equipment, maintenance engineers, and equipment experts.
A comparison of results from the evaluation or investigation against established decision criteria and/or acceptance criteria can involve adjustment of the maintenance programme. The results may also be used for making decisions regarding replacements, modifications, and upgrades of systems in a life cycle management perspective. Finally, implementation of the actions identified is a key to sustained improvement, as well as measurement of the effect via KPIs and equipment reliability data.
Learning from successes, failures and events is a key to continuous improvement of performance of a plant and an organisation. Dedicated efforts should be to implement a proactive and systematic continuous improvement process.
11 Spare parts evaluation 11.1 General
The spare part assessment defining the need for spare parts and the spare part strategy (number of, location and lead time) shall be based on results from the consequence classification (Clause 7) and other relevant analysis like reliability analysis and barrier analysis (see Subclause 4.5 for more examples). The PM programme gives the type and estimate of the demand rate for spare parts used for PM.
The demand rate and which spare parts are needed for corrective maintenance is more challenging to estimate. The typical sources are historical maintenance and inventory transactions, installation specific data, generic reliability data (e.g. OREDA®), and vendor and maintenance personnel experience. The maintenance order shall state the needed spare parts for the activity.
Further parameters such as procurement lead time and transportation time will have significant impact on the ultimate quantities of spare parts to be hold, their quantities, as well as location.
11.2 Work flow for evaluation of spare parts
Figure 6 gives an overview of the work flow for evaluation of spare parts. Subclause 11.3 to 11.5 details the content in each box.
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Spare part list / BoM
Identify unique spare parts and spare part category •
Consequence classification of equipment (clause 7)
Input to: LCC/LCP
Location and holding based on risk assessment • • • •
Demand rate from: • Preventive maintenance (clause (8) • corrective maintenance • Barrier analysis • Other (see Clause 4.5)
Output: Spare part category Location Max/min levels Re-order level
Inventory and procurement management system
Figure 6 - Evaluation of spare parts
Spare parts can be categorised as follows: • capital spare parts: − vital to the function of the plant, but unlikely to suffer a fault during the lifetime of the equipment; − delivered with unacceptably long lead time from the supplier and usually very expensive; − often these spare parts are characterised by a substantially lower cost if they are included with the initial order of the system package; − also called insurance spare part. • operational spare parts: − spare parts required to maintain the operational and safety capabilities of the equipment during its normal operational lifetime. • consumables: − item or material that is not item specific and intended for use only once (non-repairable). Spare parts from different vendors and suppliers should be registered and uniquely identified in the maintenance management system by using the OEM equipment number.
11.4 Location and holding
Spare parts are normally held at various locations. Determining the optimum location for a spare part shall be done by use of a risk model where the dimensions are consequence of not having the spare parts in place and the demand rate. See Annex C, for an example of a risk matrix for use to determine location. Demand rate can be estimated from preventive and corrective maintenance. The consequence 36
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11.3 Spare part categories
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of not having the spare part in place can be established for this purpose, or by use of the functional classification, see Clause 7.
11.5 Reorder level and order quantity
The re-order level and order quantity are important parameters to control that spare parts are available without under- or overstocking. Traditional inventory methods and formulas can be used to estimate these parameters for operational spare parts and consumables. Capital spare parts are evaluated case by case based on a risk assessment. The output is a level of spare parts which incurs the minimum combination of costs and risks.
Reorder level is based on demand rate and delivery time, adjusted by a safety factor due to uncertainty. Order quantity is estimated based on demand rate, cost per order, and holding cost.
12 Personnel and resources
In order to get quality in maintenance engineering, including consequence classification, programme development, acceptance for changes and create a basis for continuous improvements, it is necessary to involve maintenance personnel and production operators in the risk assessment and preparation of the maintenance activities. A dynamic maintenance programme requires proper documentation of the evaluations for future adjustments and improvements according to new experience and changes of operational conditions. This applies irrespective of whether GMCs are applied or the maintenance programme has been developed on basis of the RCM/RBI/SIL analysis. The following type of personnel/experience should be involved: • maintenance personnel with specific experience from different type of systems/equipment, which typically will involve mechanical, instrument, electrical and corrosion/inception qualification on senior level; • maintenance planners and/or maintenance supervisors; • operation and process personnel with process/production experience handling the production impact of a failure; • personnel with specific experience related to risk assessment and maintenance analysis – often acting as facilitators driving the process; • maintenance engineers. The above personnel may be employed by the operating organisation, by vendors or consultants.
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Annex A (informative)
Main function (MF) description and boundaries Descriptions of MFs should aim to describe an active function (i.e. ’Pumping‘ instead of ’Pump‘). Descriptions commonly used for MFs are shown in Table A.1. Normally a further specification is required to describe the MF sufficiently. If relevant, the availability, capacity and performance should be specified. Table A.1 – Examples of MF descriptions
MF description
Sub title, examples
Accumulation
Instrument/plant air, heating/cooling medium
Circulating
Heating/cooling medium
Cementing
Compressing Cooling
Detecting
Distributing Drying
Expanding
Fire and gas
(Main/emergency) power, hydraulic, tele Air, gas
Filling
Lubrication oil
Fire fighting
Sprinkler, deluge, water spray, foam, aqueous film foaming foam, hydrants
Generating Heating
Injecting
(Main/emergency) power Chemicals, gas, water
Life Saving
Mob, lifeboat, basket, raft, escape chute
Logging
Well, production, mud
Lifting
Manoeuvring Metering Pumping
Regenerating Scrubbing
Deck crane, personnel, goods
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Filtering
Fiscal (gas/oil), CO
2
Oil/gas export, bilge, seawater Glycol
Separating
Production, test, cyclone- (water/sand/oil), centrifuge
Transferring
Oil/gas pipe (riser)
Storing
38
Gas export/injection
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Chemicals, potable water, lubrication/seal oil
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Examples displaying the MF HF2020 (along with others) with boundaries marked on a flow diagram, and the same MF with boundaries marked on the more detailed P&ID is shown on Figure A.1 and Figure A.2.
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Figure A.1 – Flow diagram showing borderlines between MFs (HF2017, HF2020) --`,,```,,,,````-`-`,,`,,`,`,,`---
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Figure A.2 – P&ID showing borderlines for MF HF2020
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Annex B (informative)
Simplifying consequence assessment of standard sub functions The consequence assessment of the MF already performed may be used as a basis for establishing the consequence assessment for the standard sub functions. It is recommended that these evaluations are verified by experienced process personnel and adjusted individually, if needed. An example of guidelines for the standardised sub functions for one project is shown in Table B.1.
Table B.1 – Project guideline example of consequence assessment of standardized sub functions, based on the MF consequence assessment Standard sub function Main task
Pressure, relief
Shut down, process
Classification of loss of function RED
HSE
PROD
Other
MF
MF
MF
MF
A
H
L
L
Configuration
Shut down, equipment
MF
Monitoring
MF
Controlling
Local indication Manual shutoff
Table Key: HSE/PROD/Other H/M/L MF RED (MF)
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H
M
L
L
MF
L
L
MF
MF
MF
MF
L
L
MF
M
(MF)
L
(MF)
MF
Comment
RED: No redundancy for the failure mode ‘Fail to operate on demand’
RED: No redundancy for the failure mode ‘Fail to operate on demand’. Other: Inherits the highest consequence from the MF
L
(MF)
See examples and definitions in Annex C Consequence “High”, “Medium” or “Low” Will inherit MFs Redundancy, see definition in Table C.2. Reduce with one level from MF
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Note to entry: ’Other functions‘ have to be assessed independently.
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Annex C (informative)
Risk assessment criteria
C.1 Risk assessment using risk matrix An example of a consequence classification matrix is shown in Table C.1. The classification matrix used for maintenance purposes should be harmonized with the corporate risk matrix. For maintenance purposes it is usually sufficient to have 3-5 consequence classes, whereas a corporate risk matrix can have many more consequence classes. The different consequence categories should also be the same as used in the corporate risk matrix. The consequence classes should be aligned so the highest consequence is used for planning and prioritization. ISO 14224 gives another example of failure consequence classification.
Table C. 1 - Example of consequence classification matrix
Consequence category Safety
C1
C2
No potential for injuries.
No effect on safety systems. Environment Production
Other
No/minor spill
No production loss No operational or asset cost consequences
Containment
Cost < X (USD)
Non-flammable media Non-toxic media
Natural/normal pressure /temperature media
Potential for injuries requiring medical treatment.
Single/multiple fatality or serious personnel injuries.
Medium discharge
Major discharge
Limited effect on safety systems.
Delayed effect on production (no effect in x days) or reduced production
Moderate operational or asset cost consequences X < Cost < Y (USD)
Flammable media below flashpoint Moderately toxic media
High pressure/ temperature media (>100 bar/80 °C)
Table C. 2 – Example of redundancy definitions RED A B C
C3
Render safety critical systems inoperable. Down time loss of production DT > X days
Significant operational or asset cost consequences Cost > Y (USD)
Flammable media above flashpoint Highly toxic media
Extremely high pressure /temperature media
Redundancy degree definition No redundancy i.e. the entire system is required to avoid any loss of function. One parallel unit can suffer a fault without influencing the function.
Two or more parallel units can suffer a fault at the same time without influencing the function --`,,```,,,,````-`-`,,`,,`,`,,`---
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C.2 Decisions based on consequence classification As described in Clause 7, the consequence classification is used to plan activities and prioritize resources.
The consequence classification is used to decide the priority of a corrective work order, together with the failure mode and state of degradation. There should be a matrix in place to set the due date for each corrective work order based on the mentioned criteria. The due date can be changed to a later date then the default date due to lack of spare parts, access, personnel etc. but the priority of the work order should remain the same. To get hold of the required spare parts and resources should then also be of the same priority. If the due date is not met, this should be flagged, and in case of work order for high consequence items, be classified as a non-conformity and subject to proper follow-up and risk assessment. Table C.3 gives an example of due dates for corrective maintenance task based on the consequence classification. Table C. 3 – Example of priority/time to repair based on classification Consequence
Priority/ time to repair
Comments
High
5 days
Barrier equipment < 2 days
Medium
30 days
Low Un-Prioritized
180 days 360 days
Unclassified
Redundancy should also be taken into consideration when setting due date and prioritizing work.
C.3 Spare parts
An example of consequence classes which can be used to determine the optimum location for spare parts is given in Table C.4. Input from the consequence classification can be used or modified for this purpose. The consequence classes combined with demand rate gives location of spare parts as shown in Table C.5. Table C.4 – Example of consequence classes for spare parts
Consequence High Medium Low
Description Equipment of a system that shall operate in order to maintain operational capability in terms of safety, environment and production.
Equipment of a system that have installed redundancy, of which either the system or its installed spare must operate in order to maintain operational capability in terms of safety, environment and production. No consequence for safety, production or environment.
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Consequence
Table C.5 – Example of risk matrix for spare parts Consequence
Demand rate
Demand rate
Low
High Low
Medium
High
Not frequently used. Not frequently used.
Insurance spare Capital parts.or parts.spare Seldom Seldom or never never used.
No stock
No stock No stock
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First line spare Minimum stock Minimum stock Minimum stock at site parts. Frequently at site at site, and any First line spare parts, and any additional Minimum stock at site used. additional spare Adequate stock at site frequently used. spare parts at central parts at central warehouse warehouse Central Central warehouse warehouse, no warehouse, and Central warehouse, no and minimum stock stock minimum stockat stockatatsite site site if convenient at site if convenient No stock No stock
used.
Holding Holding optimized by optimised by use useofofrisk risk assessment case by case
by case
C.4 Risk matrix The consequence classification gives, as the term imply, the consequence in the case of loss of function. As part of performing a FMECA and RCM analysis the probability of each failure mode is defined. The probability gives an indication about the uncertainty of when the failure mode is expected to occur.
The consequence of failure and the expected failure frequency from the FMECA-analysis can be combined to establish the risk for the failure modes for each items failure mode, and the overall risk for each item.
From the FMECA/RCM-analysis the probability of the failure mode and failure mechanism is defined. If defined as part of a generic maintenance concept, when assigned to an item the total risk for the particular failure mode for the particular item is defined.
The risk is used as a basis for the maintenance interval for the defined failure mode, see Annex D.3 for an example.
When one generic maintenance concept is applied to two different items with different consequence classification or redundancy the suggested maintenance activities and intervals can be different. I.e. items with higher consequence classification will normally have more maintenance and at shorter intervals. For failure modes that do not affect the function of the item, like EX-protection, the maintenance should be the same regardless of the functional consequence classification. See Annex D.4 for an example of a generic maintenance concept.
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The expected failure frequency for each equipment and each failure mode can be calculated based on installation- or companywide maintenance records or using generic failure data from OREDA© or similar sources.
However, for practical purposes it is often better to use qualitative data and expert judgements to set an expected failure frequency, like 2-5 years, 5-10 years etc., especially for new installations or item where there is little data available to establish a quantitative failure frequency.
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Annex D (informative)
Practical examples
D.1 Technical hierarchy The level of detail with regards to tagging is in many ways a deciding factor to ensure that the equipment will receive the adequate maintenance. On the Norwegian Continental Shelf there is an industrial heritage of tagging to a detailed level where even instrumentation and equipment in support of MFs and sub functions are tagged The tagging is to be consistent from drawings, the actual equipment in the installation and the CMMS and is an important part of documenting the equipment through its life cycle. Figure D.1 illustrates the workflow to establish a technical hierarchy. Technical drawings/ P&IDs
Identify systems
Any skids or main equipment on system?
Any instruments or valves on system?
No
Yes
Yes
Use skids and main equipment as superior tag and link them to system
Establish administrative tag as superior tag and link it to system
Link instruments, valves and related equipment to corresponding superior tag
No
Any pipe lines on system?
Yes
Establish administrative tag as superior tag and link it to system
No
Go to next system
Link pipe lines to superior tag
Figure D.1 – Work process technical hierarchy --`,,```,,,,````-`-`,,`,,`,`,,`---
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To establish a technical hierarchy it is necessary with a set of technical drawings, e.g. flow and one-line diagrams, P&IDs etc. and a list of tags and a tool for linking tags to each other.
The top of the technical hierarchy normally starts with the installation code with the system numbers listed in Figure D.2. The usage of system numbers may vary from plant to plant NORSOK Z-DP-002 uses system numbers between 00 and 99. Other standards like SFI [Ship research institute of Norway (Skipsteknisk Forskningsinstitutt)] would have a 3 digit numbers as system numbering, but the principles may be similar. Technical drawings can be used to identify skids, packages and main equipment that can work as a superior tag for the connected instruments, valves and other kinds of equipment. There can be several levels beneath a level, e.g. a skid that contains 2 pumps with electric motors. The skid will then be the top level, the pumps will be the 2nd level, and the electric motors will be the 3rd level to the corresponding pump. Each level can hold corresponding instruments and valves. See Figure D.2.
Start with a system by identifying skids and main equipment. Then link all the skids and main equipment that will be used as a superior tag to the system number in the tree structure. Next step is to identify the instruments, valves and other kinds of equipment on the system and connect them to the corresponding skid or main equipment. If there are no skids or main equipment, but only e.g. instruments or valves, then administrative tags should be established to form the level above. The instruments, valves and other kinds of equipment are then linked to the administrative tags. In instrument loops one of the components can represent the whole loop e.g. a transmitter or valve, while the rest of the loop lie beneath.
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Figure D.2 – Technical hierarchy 48
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D.2 Functional hierarchy The functional hierarchy is a logical diagram linking all the plant functions noted as MF and sub functions, see Annex A. The level of detailing of the functional hierarchy may vary, but usually 2 to 3 levels are sufficient.
The plant system 27 (gas export) is shown in Figure D.3 in a schematic diagram of a plant (platform) which has been broken down into equipment identified by its tag number. The defined MFs covering part of this system and the standardised sub functions for one of these MFs are illustrated as an example.
Each tag within one sub function is given the same classification because a fault on any of these units (identified by the tag numbers) will cause the same consequence on the MF. A typical example of a consequence analysis of a MF (2701 Scrubbing), with standard sub functions listed, is shown in Figure D.4. This MF consists of two parallel units, each able to perform 100 % of the scrubbing function in relevant operating mode. Although this example identifies 100 % redundancy for this MF, redundancy is ignored at this time. For the purpose of determining the consequence class all MFs should be considered as single, irrespective of their design redundancy. The consequence classification is 3 (high), 2 (medium) and 1 (low). The degree of redundancy is set by characters A, B or C for the relevant operating mode. The degree of redundancy for sub-functions is set based on number of parallel units and capacity (Cap: 50 %, 100 %).
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D.3 Documentation of consequence analysis
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Figure D.3 – Functional hierarchy, example with standard sub function and classification
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Z-008
CONSEQUENCE OF MAIN FUNCTIONS AND ITS FUNCTIONS
System 27: GAS EXPORT AND METERING Main Function: 2701
Documents
SCRUBBING
PID: P&ID 01-01
Failure mode Does not work
Parallel Units: 2
PFD: PFD 01-01
System effect:
Not able to remove liquids from gas. Gas export system shuts down/is not available.
Capacity per unit: 100% Rev: B
Installation effect:
PU*Cap -> Red
2701 MAIN
Scrubbing
2*100 -> B
1,3,1 -> 3
2701 CONTROL
Controlling
2*100 -> B
1,3,1 -> 3
2701 IND
2701 PSD
2701 EQSD 2701 PSV
2701 VALVE 2701 PV
Local indication
Shutdown, Process
Shutdown, Equipment Pressure relief
Manual shut-off
Containment, Process Vapour
2*100 -> B 2*100 -> B
1*100 -> A 2*100 -> B
1*100 -> A 2*100 -> B 2*100 -> B
S
P
O
1
3
1
Classification
Description
Monitoring
Last updated: dd.mm.yy
Gas production is shut down. Oil production to be maintained according to tariff quotas. CO2 and environmental consequence.
Function
2701 ALARM
Redundant grade: B
(S,P,O-> Max) 2,1,1 -> 2 1,1,1 -> 1 3,1,1 -> 3 2,1,3 -> 3 3,1,1 -> 3 1,2,1 -> 2 1,3,1 -> 3
Table key Classification (S: Safety; P: Production; O: Other): 3: High
2: Medium 1: Low
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Figure D.4 – Consequence assessment of a MF. The example is shown with some key data and the classification of the sub functions listed below
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D.4 Documentation of generic maintenance concept (GMC) A GMC is a set of maintenance actions, strategies and maintenance details, which can be seen as a collection of best practices for a company. The GMC should be defined by a structured RCM analysis where failure modes and failure mechanisms are identified.
All tags should be linked to a relevant GMC and should be available for reference directly in the CMMS. Use of dummy concepts should be restricted to a minimum and only linked to tags where a detailed generic maintenance analysis has revealed no need for any maintenance activity. Equipment which is part of an instrument loop, but no concept is applicable, should be linked to same concept as the superior tag, i.e. instrumented valve.
Each concept should specify which type of equipment the concept is covering and which type of equipment that is excluded. Each concept should be detailed at such level that it provides sufficient information, as keywords or by a short description, about relevant maintenance activities and intervals of such activities in order to maintain the equipment’s intended function. It should be avoided to specify maintenance activity at the concept which is not relevant for the actual functional location which the concept is linked to.
The following table shows the final result and not the documentation of the entire process.
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Table D.1 – Generic maintenance concept Equipment class:
El. Motor < 300 kW
Responsible discipline:
E-Electrical
Applies for electrical motors independently of voltage and design
Approved by:
nn
Approved date: Object
dd.mm.yy
Activity No.
Activity group
Activity description
D
M
S
Unit
Maintenance Interval pr. Consequence class High
Motor
66030-51A
Motor
66030-02A
Motor
66030-15A
Motor
66030-71A
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Concept note:
51 Lubrication
02 Near visual check 15 Measurement 71 Overhaul
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Lubrication of el.motor
For outside motors, check external and internal condition of junction boxes. If the JB has flame slits, check and lubricate. Megger test stator and rotor windings Overhaul of electrical motor
Medium
Duration
Work load Resource x time
Low
Total man hours
MECH
N
N
M
3
6
-
0,5
MECH x 0,5
0,5
ELEC
N
N
M
12
12
12
1,5
ELEC x 1,5
1,5
ELEC
N
Y
M
12
12
12
0,5
MECH x 0,5
0,5
ELEC
N
Y
H
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24000
48000
-
20
2 x ELEC x 20
40
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Failure mode analysis: Preventive Activity(s)
Failure Mode
66030-02A, 66030-71A
SPO - Spurious operation
Failure Mechanism
Failure Cause
Frequency (yrs/failure)
Analysis Reference
Wear
Wear
5-10 Years
Project
Loss of function
Voltage unbalance
> 20 Years
OREDA
Degraded Function
OREDA
Degraded Function
66030-15A
FTS - Failure to start on demand
General electrical failure
Protection trip due to overcurrent, overload & short circuit
66030-51A
ELU - External Leakage
Vibration
66030-15A, 66030-71A
LOO - Low output
66030-51A
STD - Structural deficiency
66030-02A
OHE - Overheating
66030-51A
66030-02A, 66030-71A
Legend:
D) Discipline
M) Requirement from government/company
S) Shutdown
Equipment class
VIB - Vibration
FRO - Failure to rotate
5-10 Years
OREDA
Bearing friction, lubrication
5-10 Years
OREDA
Vibration
Bearing fracture/fault
2-5 Years
General material failure
Mechanical damage
General electrical failure Vibration
General material failure
Winding failure
Bearing fracture/fault
5-10 Years
5-10 Years 5-10 Years
Project Project Project
Local Effect
Hidden Failure Y
Loss of function
N
Degraded Function
N
Degraded Function Unsafe failure
Loss of function
N
N N Y Y
Craft/competence (e.g. MECH: mechanic, ELEC: electric, OPER: operator) Regulations and company requirements. For barrier functions:
- Safety critical failure with connected testing interval - SIL requirement (acceptance level)
Shutdown required to undertake repair, and possibly production shutdown depending on redundancy and HSE requirements ISO 14224 provides a recommended structure for equipment class --`,,```,,,,````-`-`,,`,,`,`,,`---
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Operating and frame conditions
Physical operating and frame conditions for the concept
Revision
Revision number
Consequence class
Activity description Ref to main doc
Maintenance Interval Interval unit
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Responsible person/discipline for this concept
Consequence class for maintainable item from consequence classification Description of PM activities
Reference to detailed description of maintenance activity
Generic maintenance interval established based on consequence classification, operating conditions etc.
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Responsible
Months, years, hours etc.
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Bibliography API RP 580,
Risk-Based Inspection
DNVGL-RP-F116,
Integrity management of submarine pipeline systems
DNVGL-RP-G101,
Risk Based Inspection of Topside Static Mechanical Equipment
EN 15341,
Maintenance – Maintenance Key Indicators, Edition 1, Jul. 2007
DNVGL-RP-0002,
Integrity management of subsea production systems
DNVGL-RP-F206,
Riser integrity management
EN 13306,
Maintenance – Maintenance terminology, Edition 1, Nov. 2010
ISO 12100,
Safety of machinery – General principles for design – Risk assessment and risk reduction, Edition 1, Jan. 2011
ISO 15663-1,
Petroleum and natural gas industries - Life cycle costing – Part 1: Methodology, Edition 1, Sep. 2009
ISO/TR 12489,
Petroleum, petrochemical and natural gas industries - Reliability modelling and calculation of safety systems, Edition 1, Nov. 2013
IEC 60050-192
Electrotechnical vocabulary Part 192 Dependability, Edition 1.0, 2015
NOG 122,
Recommended guidelines for the assessment and documentation of service life extension of facilities
NORSOK S-002,
Working environment, Edition 4, Aug. 2004
Basisstudien
Basisstudie vedlikeholdsstyring, Ptil, 1998
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Coding system, Edition 3, Oct. 1996
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[email protected] www.standard.no
[email protected] www.standard.no
Telephone +47 67 83 86 00
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